Electropolymerization Of The Conducting Polymer PEDOT In Zwitterionic Surfactant Self-assembly System

Poly(3,4-ethylenedioxythiophene)(PEDOT)is an organic polymer material with unique optical/electrical properties.Due to the poor water solubility of the monomer EDOT,the electrochemical preparation of PEDOT is traditionally carried out in molecular organic solvents.Considering the adverse effects of molecular organic solvents on human beings and the environment,the green electrochemical preparation of PEDOT has received considerable attention.Water is an environmentally friendly and low-cost reaction medium.Relevant studies have shown that the addition of surfactants can increase the solubility of EDOT in water,but the doping of the surfactants can also affect the redox activity of the polymer PEDOT.Compared to aqueous micellar solutions,ionic liquids have a strong ability to dissolve EDOT,low vapor pressure,and good conductivity,making them very suitable for use as reaction media for electropolymerization of PEDOT.However,the expensiveness and the high viscosity of ionic liquids limit their wide application in the field of electrosynthesis of conducting polymers.The construction of an ionic-liquid-based microemulsion with surfactant is a good strategy to solve the above problems,and there are few reports on this aspect.Considering that the zwitterionic surfactant is electrically neutral and not easy to be electro-oxidized,the electropolymerization of PEDOT in zwitterionic surfactant selfassembly system is worth studying.To this end,the following two works have been carried out:1.Green and efficient electrosynthesis of PEDOT in aqueous micellar solution of zwitterionic surfactantA biodegradable zwitterionic surfactant SB3-14(n-tetradecyl-N,N-dimethyl-3-ammonio1-propanesulfonate)was chosen to solubilize the poorly water-soluble monomer EDOT,and in the micellar solution of SB3-14,the anodic polymerization of EDOT was studied to demonstrate the advantage of the zwitterionic surfactant over the nonionic surfactant.Compared with the reported nonionic surfactant polyoxyethylene-10-laurylether(C12E10),SB3-14 is neither adsorbed on the glassy carbon electrode(GCE)over-0.2～1.0 V vs.SCE,nor oxidized at the high oxidative polymerization potential for EDOT.These unique properties are favorable not only for the enhancement of the electropolymerization rate,but also for the improvement of the current efficiency.A comparative study on the electropolymerization modes,i.e.,the constant potential mode and the pulsed potential mode,indicates that at high oxidative polymerization potential,the EDOT electropolymerization reaction is limited by the diffusion mass transfer of the electroactive monomer,and the growth rate of the polymer PEDOT can be significantly increased by prolonging the duration time of the pulse lower limit potential.At low oxidative polymerization potential,however,the EDOT polymerization reaction is basically controlled by the heterogeneous charge transfer process,and the electropolymerization modes have little effect on the growth rate of the PEDOT film.The XPS data of the PEDOT films demonstrate that SB3-14 is not doped(encapsulated)into the PEDOT film,and ClO4-is the only doping species.The doping level of the PEDOT film is determined by the oxidative polymerization potential and the electropolymerization mode.At high oxidative polymerization potential,the pulsed potential mode results in a PEDOT film with higher doping level than the constant potential mode does due to the periodic relaxation of the monomer concentration gradient as well as the full doping of the polymer in the duration time of the pulse lower limit potential.The above studies demonstrate that this new strategy is helpful for the green and efficient electrosynthesis of high quality PEDOT.2.Electropolymerization of EDOT in hydrophobic ionic liquid based microemulsion stabilized by zwitterionic surfactantAn attempt has been made to carry out the electropolymerization of EDOT in the zwitterionic surfactant(SB3-12)stabilized H2O/[C6mim][PF6](1-hexyl-3-methylimidazolium hexafluorophosphate)microemulsion.To explore the influence of water content(i.e.,microstructure)of SB3-12/H2O/[C6mim][PF6]microemulsion medium on the EDOT electropolymerization,the phase triangle was determined at 25℃,and a series of SB3-12 stabilized H2O/[C6mim][PF6]microemulsions with different water contents were prepared accordingly.The viscosity,conductivity and electrochemical window of the microemulsion and its solubilization capacity toward EDOT were measured.The results show that the present SB3-12 stabilized ionic liquid microemulsion is suitable for use as the reaction medium for electropolymerization of EDOT.Studies on the electropolymerization behavior of EDOT in this[C6mim][PF6]-based microemulsion show that the water content of the microemulsion medium not only significantly affects the onset potential and the electropolymerization rate of the PEDOT,but also changes the morphology and the doping level of the as-prepared PEDOT.XPS data show that the PEDOT prepared in the high water content microemulsion has a higher doping level.The use of the ionic liquid microemulsions can reduce not only the amount of expensive ionic liquid,but also the onset potential for the electrooxidation of EDOT.Moreover,by tuning the water content of the ionic liquid microemulsion,the electrochemical performance of PEDOT could be regulated accordingly.Under the identical deposited charge,the PEDOT prepared in the high-water content microemulsion(79.7%H2OμE)has higher specific capacitance(107 F g-1)than that in neat[C6mim][PF6](103 F g-1).It follows that the present ionic liquid microemulsion is a good medium for EDOT electropolymerization.This study provides a new strategy for the synthesis of high-quality PEDOT film in a green and low-cost reaction medium.